A forming box of the type described in EP 0 159 618 A1 is most often an integral part of the entire papermaking plant, and constitutes an essential limitation to the capacity of the plant.
Fibers are blown into a forming box, where they are distributed onto an underlying forming wire. A vacuum box is provided underneath the forming wire for drawing the fibers onto the forming wire. For placing the fibers on the forming wire, the forming box is provided with a bottom net or sieve having a number of openings. In order to ensure the passage of the fibers through the bottom of the forming box it is suggested to use wings, rollers or other scraping or brushing devices, which in an active manner removes fibers from the sieve at the bottom of the forming box. Although such mechanical devices do give an increase in manufacturing capacity, attempts have been made for many years to increase the capacity further.
The size of the openings in the mesh or sieve at the bottom of the forming box depends upon the characteristics of the fibers which are to be distributed on the forming wire. This is particularly relevant in relation to the use of cellulose fibers in the manufacture of paper products including absorbing products, such as napkins. Thus, there has been a limitation in the length of the fibers used. In practice, it is found that it is generally not possible to use fibers with a length of more than about 18 mm. This also limits the kind of non-woven products that can be thus manufactured.
U.S. Pat. No. 6,233,787 B1 describes a forming box with an open bottom, i.e. without a bottom mesh or sieve. The distribution of fibers is carried out by a number of rotating spike rollers in the forming box, the spikes being arranged to partly hold back the fibers against the effect of the aid stream resulting from the suction of the underlying vacuum box. The cloud of fibers which is formed inside the forming box of single fibers, which are mixed in the air stream, are transferred down onto the underlying wire by the application of the rotating spike rollers. This increases the capacity of the forming apparatus.
However, clumps of fibers may pass the spike rollers without being tom sufficiently apart by the spikes. This results in an uneven distribution of fibers on the forming wire. It would be desirable to provide a fiber distributor which encourages an even distribution of fibers on the forming wire in a dry-forming apparatus without compromising the capacity of the fiber distributor. In addition, it is the object to provide a fiber distributor which is reliable in operation and which allows for longer time between overhauls or maintenance.